This invention relates to a data communication system in which data to be transferred is converted or modulated to digital pulse-coded transmission data including two pulse signals having different pulse durations and the digital transmission data is sent through a transmission path from a transmitting end to a receiving end where the received data is demodulated.
In a conventional data communication system, signal transfer over a long distance with high stability must overcome not only voltage drops due to signal attenuation through the transmission path but also the interference between codes due to the frequency dependence of the signal attenuation factor for the transmission path. Generally, such a signal attenuation factor in the transmission path proportionally depends upon the frequency of the signal. For example, in the case where two digital signals having different pulse durations are sent through the transmission path, the attenuation factor of the longer pulse duration signal is smaller than that of the shorter pulse duration signal so that the data reproduced at the receiving side is distorted. This distortion causes a degradation of the S/N ratio and transmission quality.
The article entitled "A Bipolar Repeater for Pulse Code Modulation Signals" by J. S. MAYO in THE BELL SYSTEM TECHNICAL JOURNAL, January 1962, pages 25-51 discloses nonlinear equalization according to which a series circuit of an inductance and a resistor is connected across transmission cable lines in order to reduce the signal distortion which may occur through the transmission cable (especially see page 45 of this Journal).